will a verizon 4s, since its called on world phone work on other networks such as gsm? since it's a world phone now? i can switch to any carriers? or its only a world phone for cdma worldwide?

It will work on GSM if you have that feature enabled. It will *roam* on other GSM carriers (probably not in the US) and you would have to pay the very expensive roaming fees. The question is whether Verizon will allow the phone to be unlocked so you can use other carriers SIM cards abroad.

so if i get a cdma 4s unlocked i can switch to at&t when my contract is over

Mmm, hard to know!

1) You can, in November, buy unlocked iPhones 4S from Apple, however these will not work on CDMA, so that is probably not what you want to do.

2) If you buy a standard one from Verizon, AND they are willing to unlock it, you will be able to use GSM abroad. Note we don't know if this will happen, AT&T has refused to unlock iPhones whereas they will unlock their other phones. I don't know if this was a decision with Apple or just to maintain their then sole-vendor status.

3) The issue is using it in the US on AT&T. Some of the world phones, in particular those from Motorola, have a carrier-band-lock. These prevent you from using GSM carriers in the US with any SIM. On the other hand, the HTC Droid Incredible 2 doesn't have this band lock, and once you unlock that phone, you can use AT&T (you don't need to wait for your contract to end, but of course you are then going to be paying Verizon for the monthly service and AT&T for the use of AT&T!)

So the answer to your question depends on first if the phone will be unlocked at all, and then whether it follows the Motorola or HTC model for carrier band unlock.